Mortgage trouble is creating some of the biggest bargains this side of eBay, allowing buyers to snap up homes for tens of thousands of dollars less than what they might have paid just a few months ago. "People are doing whatever they can to sell" in order to avoid foreclosure, said Brad Geisen, president and chief executive of Boca Raton-based Foreclosure.com. Notices of pending foreclosures are piling up, in what many believe to be the first wave of a trillion-dollar tsunami: The dollar volume of home loans with interest rates that will be ratcheted upward over the next several months....